Rigid base earth compactor

ABSTRACT

An earth compactor having a unitary base with downwardly facing convex surfaces. A first vibrator assembly is mounted generally centrally of one surface and a second vibrator assembly is mounted generally centrally of the second surface. Each assembly includes an eccentrically mounted weight. The weights are rotated at a speed ratio of 2:1 relative to each other and are initially positioned so both weights are up relative to the shafts on which they rotate. Such phasing of the weights provides an upwardly directed simultaneous unweighting action which facilitates steering and moving the machine by an operator. In one embodiment the weights have the same mass. The impacts exerted on the earth by this machine have a complex waveform, including a band of frequencies which provide for optimum compacting of earth of various particle sizes and consistencies. In a second embodiment the slower rotating weight has a greater mass than the faster rotating weight. In another embodiment, the portion of the base associated with the slower rotating heavier weight is heavier than the portion of the base associated with the lighter faster rotating weight.

United States Patent Kaltenegger [54] RIGID BASE EARTH COMPACTOR [72] Inventor: Benno Kaltenegger, Kurhausstr, 77-

79, 5202 Hennef, Germany [22] Filed: Dec. 15, 1970 [21] Appl. No.: 98,328

[30] Foreign Application Priority Data Great Britain ..94/48 [451 Nov. 21, 1972 Primary ExaminerJacob L. Nackenoff Attorney-Markva, Smith & Kruger [5 7 ABSTRACT one embodiment the weights have the same mass. The

impacts exerted on the earth by this machine have a complex waveform, including a band of frequencies which provide for optimum compacting of earth of various particle sizes and consistencies. In a second embodiment the slower rotating weight has a greater mass than the faster rotating weight. In another embodiment, the portion of the base associated with the slower rotating heavier weight is heavier than the portion of the base associated with the lighter faster rotating weight.

21 Claims, 7 Drawing Figures memeuavvel 1912 3.703. 1 2 1 SHEET 1 BF 2 INVENTOR gsfnmxr KW MAM "KW RIGID BASE EARTH COMPACTOR This invention relates to an earth compacting machine of the type in which a base is resiliently connected to a frame and the machine is equipped with apparatus to vibrate the base plate.

Earth compacting machine in which a base or base plate is vibrated by an unbalanced shaft carrying eccentrically mounted weights are known in the art. Usually, such machines have a single vibrator and a base plate with a relatively small compacting area.

Increase of the size of the compacting area of known machines has been accomplished by coupling several such prior art machines together. In the usual arrangement, the upper or frame parts of the machine are rigidly connected together and provided with a loading weight which may be formed in part by the driving motor. The bases, or base plate of the vibrators, however, move independently of each other. Such constructions are merely variations of the machine with a single vibrating base and no particular advantage is achieved by connecting several of these devices together except that a larger earth surface can be compacted in one operation. A disadvantage of such an arrangement is that the couplings are expensive and are heavily stressed during operation of the machine.

It is an object of the present invention to provide an earth compactingmachine of improved efficiency, low cost, and without the disadvantages of the prior art devices.

Accordingly, the present invention relates to an earth compacting machine in which the base of the machine is in one piece and has at least two shafts each provided with an unbalanced eccentric weight. The base takes the form of a shell or plate having two con vex bottom surface portions, one adjacent the other in the longitudinal direction of the machine, and an unbalanced weight is associated with each convex surface.

As a result of this construction, the base provides a high specific surface pressure even though the area of the base is large. The high surface pressure is provided in part by the convex bottom surfaces of the base plate. These convex surfaces are arranged one after the other in the longitudinal direction of the machine and correspond in number to the number of shaft and weight assemblies on the rigid base. By virtue of this arrangement, the compacting action of the earth compacting machine of this invention is comparable with the action of and the efficiency of a revolving drum type road roller.

It has been found that earths of different consistencies and types should be compacted at different vibrational frequencies for optimum compacting efficiency. For example, gravel is most efficiently compacted at a different vibrational frequency from soft loamy soil. In order to achieve the best possible results it has been necessary in the past to have available several machines, one to compact gravel, for example, and one to compact soft loamy soil. In accordance with this invention, only one machine is required because the machine produces a wide band of frequencies within predetermined limits and these frequencies are constantly repeated. Since these different frequencies occur repeatedly, and since different earth particle sizes respond differently to different vibrational frequencies, substantially all the particle sizes in the earth are vibrated and compacted with equal efficiency. Because of the various harmonics resulting from vibrating the base of the machine of this invention, earths of different consistencies are compacted as efficiently as if an optimum frequency were selected for compacting the particular earth. Correspondingly, a single machine in accordance with this invention is suitable for compacting earth of various consistencies with the same optimum operating action. In accordance with one feature of the earth compacting machine of the invention, optimum vibrational and impacting characteristics are attained by rotating the weights at different rotational speeds relative to each other to provide frequencies and amplitudes for optimum compacting action.

The construction of the earth compacting machine of the invention is such that even though the 'base plate is rigid and of unitary construction, the individual convex surface portions of the base plate are subjected to vibrations of different frequencies. Such vibrations are transmitted to the earth through the associated bottom surface portion of the base. For example, if one weight is rotated to vibrate at a frequency of 60 cycles per second and the other weight is rotated to vibrate at cycles per second, the result is that one convex bottom surface impacts the earth with the lower primary frequency. By rotating one shaft so its associated weight vibrates at one frequency, and rotating another shaft so its associated weight vibrates at a different frequency, but related to the first frequency, the vibrational impacts on the earth are displaced from each other in time but occur in a predetermined sequence.

The shafts and the associated unblanced or eccentric weights are so selected as to provide the desired frequency ranges. Advantageously, the weight on one shaft can be heavier than the weight on another shaft and the heavier weight will be rotated at a speed so its frequency of vibration is lower than the frequency of vibration of the shaft with the lighter weight. In addition, the shaft with the lower frequency larger weight, can be associated with a heavier bottom surface portion of the base with, for example, the ratio of the mass of the heavier bottom surface to the mass of the lighter bottom surface in the same ratio as the mass of the larger weight to the mass of the smaller weight. By

proper selection of the sizes of the rotating weights relative to the mass of the base plate, the intensity of the vibration from either the high frequency weight or the low frequency weight can be carefully regulated. By virtue of such an arrangement, the proper frequency range for the earth to be compacted can be obtained quite simply by varying the mass of the weights, changing the rotational speed of the weights, or using base portions in which the convex surfaces are of different mass.

Numerous other objects, features and advantages of this invention will become apparent with reference to the drawings which show several preferred embodiments of the invention and in which:

FIG. 1 is a diagrammatic partial sectional view in side elevation showing one embodiment of earth compacting machine according to this invention;

FIG. 2 is a partial view corresponding to FIG. 1 and showing a different embodiment;

FIG. 3 is a view corresponding to FIG. 2 and showing another embodiment of the invention;

FIGS. 4-7 are diagrammatical views in side elevation showing the respective positions of the unbalanced weights relative to each other during a complete cycle of rotation of one of the weights for a particular embodiment of the invention.

Referring now to the drawings in detail, and particularly to FIG. 1, earth compacting machine 1 includes a unitary one piece base member or plate 2 on which a common frame 4 of the machine is supported and which frame is mounted on the base by sets of springs 5 and 6 adjacent opposite ends of base 2. Mounted on base 2 are two vibrating assemblies 7 and 8. Assembly 7 includes a shaft 9 journalled for rotation on the base and to which an eccentrically mounted weight 11 is fixed so it rotates with the shaft. Assembly 8 includes a shaft 10 also journalled for rotation on the base and to which an eccentrically mounted weight 12 is fixed so it rotates with the shaft. In the embodiment of FIG. 1, the weights 11 and 12 have the same mass, shafts 9 and 10 are parallel, and the shafts 9 and 10 extend transversely of the machine.

Mounted on frame 4 is a motor 13 which drives shaft 9. The drive arrangement includes a pulley 14 keyed to the motor shaft, and a pulley l5 keyed to shaft 9, and a drive belt 16 which extends around the pulleys. Advantageously, a spring loaded belt tensioning device 19, mounted on frame 4, engages the belt 16 and maintains proper tension in the belt even though base 2 vibrates relative to frame 4 and the motor 13.

Shaft 10 is driven by shaft 9. The drive includes a drive belt extending around a pulley a keyed to shaft 9 and a pulley 18 keyed to shaft 10. Advantageously, pulley 18 has a larger diameter than pulley 15a so shaft 10 and its associated weight 12 rotate at a slower speed than shaft 9 and its associated weight 11. In the embodiment shown at FIG. 1, the diameter of pulley 15a is one-half the diameter of pulley 18 and correspondingly, shaft 9 rotates at a speed which is twice the speed of rotation of shaft 10. It is however within the contemplated scope of this invention to use different pulleys 15a and 18 or pulleys 15a and 15 which are of variable diameter so the ratio of the speed of rotation of shaft 9 relative to shaft 10 can be any desired value, for example 2:1, 1:1, or 1:2.

In the rotational position shown at FIG. 1, weights 1] and 12 are 90 out of phase and hence, the vibrational forces of the weights do not act in the same direction. Because weight 12 rotates at half the speed of weight 11, the frequency of vibration of assembly 8 is half the frequency of vibration of assembly 7.

Base 2 is advantageously formed from metal such as cast iron or steel and takes the form of a rigid one piece shell. As shown at FIG. 1, the base has a pair of curved bottom portions each integral with the base which provide downwardly facing convex bottom surfaces 3a and 3b arranged one after the other in the longitudinal or fore and aft direction of the earth compacting machine. Convex surfaces 3a and 3b are each arcuately curved as viewed in side elevation at FIG. 1, and are elongated in a direction transeversely of the machine so each surface is cylindrical. Convex surface 30 is associated with.

vibration assembly 7 whereas convex surface 317 is associated with vibration assembly 8. Advantageously,

the axis 21 of the center of curvature of surface 3a is perpendicular to a vertical line 22 perpendicular to the axis of shaft 9. Similarly, the axis 23 of the center of curvature of convex surface 3b is perpendicular to a vertical line 24 perpendicular to the axis of shaft 10. In the embodiments disclosed herein the axes 21 and 23 are above the axes of rotation of the respective shafts 9 and 10 so the machine 1 has a low profile.

In the embodiment shown at FIG. 1, the portion of base 2 on which surface 3a is formed is essentially the mirror image of the portion of the base on which surface 3b is formed, these portions are of essentially the same radius of curvature and have the same wall thickness, and correspondingly, these portions are of essentially equal mass and weight.

The embodiment of the invention shown at FIG. 2 is basically similar to that of FIG. 1 since the bases 2 are identical. However, the eccentric or unbalanced weight on the shaft 10 of the embodiment of FIG. 2 is heavier than the weight 12 on the shaft 10 of the embodiment of FIG. 1. (While the weight 11, the weight 12 and the weight 12a have been referred to singularly, it is to be understood that each weight could in fact be a plurality of weights spaced along the respective shafts 9 and 10.) By virtue of the arrangement of pulley 15a and 18, it is apparent that shaft 9 and weight 11 are driven at a higher speed of rotation than the speed of rotation of shaft 10 and weight 12a. Hence, the heavier weight 12 is rotated at a lower speed than the lighter weight 11, and correspondingly, the frequency of vibration of the vibration assembly including shaft 10 and weight 12a is lower than the frequency of vibration of the assembly including shaft 9 and weight 11. However, because weight 12a is of a greater mass than the weight 11, the amplitude or force of vibration resulting from the rotation of weight 12a is greater than the amplitude or force of vibration resulting from the rotation of weight 11.

Now consider the embodiment of FIG. 3. The embodiment of FIG. 3 includes the weight 12a explained with regard to FIG. 2. In addition, there is a convex surface 3a on one portion of the base identical to the convex surface 3a previously explained for the embodiments of FIGS. 1 and 2. However, a convex surface 3c is formed on a portion of the base, of greater thickness than the portion of the base on which surface 3b is formed. By virtue of this thicker wall construction on which surface 30 is formed, this portion of the base is substantially heavier than the portion of the base on which the surface 3a is formed. Correspondingly, the heavier slower rotating weight 12a on the shaft 10 vibrates the heavier portion of the base on which surface 3c is formed, whereas, the lighter weight 1 1 rotatable with shaft 9, vibrates the lighter portion of the base on which the surface 3a is formed, but at a higher frequency. In the embodiment of FIG. 3, heavier springs 6 can be used on the portion of the base 3c to support the machine frame 4.

Depending on the primary conditions of use for a particular earth compacting machine constructed according to this invention, the ratio of the speed of rotation of the shafts 9 and 10 can be any desired value most suitable for the conditions of the earth to be compacted. In addition, while the embodiment of FIG. 3 shows a heavier weight 12a associated with the heavier portion of the base on which the surface 3c is formed and while the lighter weight 11 is associated with the lighter portion of the base on which surface 3a is formed, weight 12a could of course be of smaller mass than weight 11 without departing from the contemplated scope of this invention.

While the embodiments of FIGS. l-3 show only two vibrating assemblies 7 and 8 associated with the respective convex surfaces 3a and 3b, additional vibrating assemblies each associated with an additional portion of the base on which a convex surface is formed can also be provided. These additional convex surfaces will, of course be rigid with the base portions on which surfaces 3a and 3b are formed. In addition, where the base is formed with portions having, for example, three convex surfaces, one of the surfaces can be on a portion of the base with a wall thickness like that on which surface 3a is formed, another surface can be on a thicker wall portion like that on which surface 3c is formed, and the third portion of the base could have a wall portion that is even thicker than the wall portion for surface 30.

In the embodiments as shown in FIGS. 1-3, shafts 9 and 10 each rotate in a clockwise direction. With reference to FIGS. 4-7 the preferred rotational displacement of the weights will now be explained.

With reference to FIG. 7, it will be observed that weight 11 which has the smaller mass, and weight 12a which has the larger mass, simultaneously occupy positions wherein the center of gravity of these weights are directly above or on top of the respective axes of the shafts 9 and 10. However, as previously explained, shaft 9 rotates at a speed which is twice the speed of rotation of shaft 10. Correspondingly, when shaft 9 and weight 11 have rotated 180 to the position of FIG. 4 where the center of gravity of weight 11 is immediately below the axis of shaft 9, weight 12a has only rotated 90 so its center of gravity is directly to the right of the axis of shaft 10. When weight 11 and shaft 9 have rotated an additional 180 to the FIG. 5 position, the center of gravity of weight 11 is again directly above the axis of shaft 9, whereas shaft 10 and weight 12a have only rotated an additional 90 so the center of gravity of weight 12a is now immediately beneath shaft 10. After another 180 of rotation of weight 11 to the position of FIG. 6, the center of gravity of weight 11 is again below shaft 9 whereas weight 12a has only rotated an additional 90 so its center of gravity is horizontally to the left of shaft 10. Upon another 180 of rotation of shaft 9 and weight 11, weight 12a is correspondingly rotated an additional 90 and both weights are again in the position of FIG. 7 with their centers of gravity vertically above the respective shafts 9 and 10.

The relationship shown at FIGS. 4-7 of course applies for the pulley arrangement previously disclosed wherein shaft 9 rotates at a speed which is twice the speed of rotation of shaft 10. With this speed ratio of 2:1 it is to be noted with particularity that in no relative rotational position of the two weights do the weights act either horizontally outwardly simultaneously or horizontally inwardly simultaneously. This phasing of the weights substantially reduces stresses acting on the shafts and bearings of the machine as well as on machine frame 4 and base 2. An additional advantage of this arrangement wherein weights 11 and 120 are simultaneously up at least once during two complete rotations of weight 11 is that simultaneous upwardly directed unweighting forces act on the base and facilitate steering the machine by use of a handle such as the handle 20, FIG. 1. Hence, where the compactor is of the manually steered type, an operator can easily move and steer the machine at the instant that the base is unweighted by simultaneous movement of the weights 11 and 12a to the FIG. 7 position, even though the weight of the machine is sufficiently great that the operator could not normally move the machine at all. While the operation of the machine has been explained with reference to the weights l1 and 12a, it is to be understood that where a weight 12 is used which has a mass the same as the weight 1 l, the rotational sequence and phasing of the weights will of course be the same.

While the operation has been explained with reference to FIGS. 4-7 in an embodiment in which the speed of rotation of weight 11 is twice the speed of rotation of weight 12a, various other speed ratios between the shafts l0 and 11 will provide the similar advantageous results.

For example, speed ratios between shafts 9 and 10, in addition to the ratio of 2:] previously described, may be 3:1 or 4:1 or virtually any integer ratio. It will also be appreciated that ratios of 1:2, 1:3 etc, in the speed ratio of shafts 9 and 10 will also provide similar advantages.

By virtue of the rigid base 2, convex surface 30 is not vibrated at precisely the same frequency of vibration as vibration assembly 7, and surface 3b is not vibrated at precisely the same frequency of vibration as vibration assembly 8. Instead, some of vibration from vibration assembly 8 is received by the surface 3b of the base. Hence, the impacts delivered to the earth by the surface 3a are of a frequency and amplitude which depend in part on the frequency and amplitude of vibration of vibration assembly 7 and depend in part on the frequency and amplitude of vibration of vibration assembly 8. The amplitude and frequency of vibration of the impacts on surface 3b on the earth similarly depend on both the amplitudes and frequencies of vibration of the vibration assemblies 7 and 8. In the case of the embodiment of FIG. 1, where weights l1 and 12 are of equal mass, and weight 12 rotates at a speed one-half the speed of rotation of weight 11, it has been shown that the vibrational forces from the weights 11 and 12 are in phase only once during each revolution of the weight 12 and that these in phase forces are upwardly directed. Even though the wave forms for the vibrations of the weights 11 and 12 can be represented by simple sign waves, the resultant of these sign waves is a very complex wave form which has been found to include a band or range of frequencies for each of the surfaces 3a and 3b. Hence, the ultimate effect of vibrating the rigid base plate with the assemblies 7 and 8 arranged as previously described, even where the weights have the same mass, is to vibrate the respective base surfaces at a primary frequency with side bands both above and below the primary frequency.

In the embodiment of FIG. 2 where the weights 11 and are of a different mass the amplitudes of vibration of the assemblies 7 and 8 are different from the embodiment of FIG. 1 and the wave form of vibration of the surface 3a and 3b is again quite complex. Where the base has a thicker section on which the surface 30 is formed, as shown for the embodiment of FIG. 3, the

wave forms of the vibration are again complex and the vibrations are distributed differently between the impacting surfaces.

Where there are more than two convex surfaces such as the surfaces 3a and 3b, and there is a third vibrating assembly in addition to the assemblies 7 and 8, suffice it to say that the vibrations of the several surfaces of the rigid base have a wave form which is even more complex as are the side band frequencies of the ground impacting surfaces of such an arrangement.

In each instance, however, each surface vibrates in a range of varying frequencies in a recurring pattern above and below the primary frequency of vibration for the surface, and these varying frequencies provide the frequency and amplitude of impact required to compact soils of varying consistencies with a single machine. Surprisingly, such varying frequencies occur even though weights l1 and 12a are rotated at constant, although different speeds.

While several preferred embodiments of the compacting machine according to this invention have been shown and described herein, it is to be understood that numerous changes can be made in the constructions of the preferred embodiments without departing from the scope of this invention as specified herein and as defined in the appended claims.

What is claimed is:

1. A vibratory earth compacting machine including a rigid base plate comprising:

a. a first bottom surface, and

b. a second bottom surface spaced longitudinally of the machine from said first surface,

0. both surfaces being arranged to contact said earth for compaction;

d. a first weight eccentrically mounted for rotation about a first axis transverse to the machine and generally centered over said first surface,

e. a second weight eccentrically mounted for rotation about a second axis transverse to the machine and generally centered over said second surface;

f. first means to rotate said first weight for producing vibrations at a first frequency;

g. second means to rotate said second weight for producing vibrations at a second frequency different from said first frequency;

h. said rotating means including drive means for simultaneously rotating said weights in a predetermined periodically recurring pattem such that both weights occupy the same angular position on their respective axes at least once during several revolutions of one of the weights;

said weights cooperating to vibrate said first surface of said rigid base plate at frequencies including a band of periodically recurring frequencies; and j. said weights cooperating to vibrate said second surface of said base plate at frequencies including a band of periodically recurring second frequencies different from said first frequencies.

2. A vibratory earth compacting machine according to claim I wherein said first weight is adapted to rotate at an essentially constant speed;

said second weight is adapted to rotate at an essentially constant speed which is one-half the speed of rotation of said first weight; and both weights occupy the same vertical position on their respective axes at least once during several revolutions of one of the weights. 3. A vibratory earth compacting machine according to claim 1 wherein said first surface of said base plate is convex; said second surface of said base plate is convex; and said second weight has a greater mass than said first weight. 4. A vibratory earth compacting machine according to claim 2 wherein said second surface is on a portion of the base plate having a greater mass than the portion of the base plate having said first surface. 5. A vibratory earth compacting machine comprismg:

a. a rigid base plate having a plurality of arcuate convex bottom portions formed in said plate and arranged to contact the earth for compaction, said arcuate portions extending transversely to the machine and being disposed longitudinally with respect to each other, vibrating means mounted on said base plate for vibrating said plate, and said vibrating means being disposed in spaced relation above said arcuate portions. 6. A compacting machine as defined in claim 5 wherein a rigid frame member is spaced above said base plate, said frame member being supported by spring means from said base plate. a 7. A compacting machine as defined in claim 6 wherein a power drive means is mounted on said frame member to drive said vibrating means. 8. A compacting machine as defined in claim 5 wherein said vibrating means includes a vibrating mechanism disposed above each said arcuate portion. 9. A compacting machine as defined in claim 5 wherein said arcuate portions include a first arcuate portion having a greater mass than a second arcuate portion. 10. A compacting machine as defined in claim 5 wherein said vibrating means includes a first vibrating means and a second vibrating means, said first vibrating means includes a first weight eccentrically mounted for rotation about a first axis, and said second vibrating means includes a second weight eccentrically mounted for rotation about a second axis. 11. A compacting machine as defined in claim 10 wherein said first axis is disposed in a vertical plane which includes the center of curvature of a first arcuate portion, and said second axis is disposed in a vertical plane which includes the center of curvature of a second arcuate portion.

12. A compacting machine as defined in claim wherein said vibrating means includes a first vibrating and a second vibrating means, and means to operate said first and second vibrating means at different frequencies. 13. An earth compacting machine according to claim 9 wherein said vibrating means includes a first and second vibrating means, and means for operating said second vibrating means at a higher frequency than said-first vibrating means. 14. A compacting machine as defined in claim 9 wherein said vibrating means includes a first vibrating means and a second vibrating means, and means to operate said first and second vibrating means at different frequencies. 15. An earth compacting machine according to claim 12 wherein said first frequency is approximately one-half second frequency. 16. An earth compacting machine according to claim 12 wherein said first means includes a first weight mounted eccentrically for rotation; said second means includes a second weight mounted eccentrically for rotation; and said operating means includes means to rotate said weights at different speeds relative to each other. 17. An earth compacting machine according to claim 0 10 wherein said first weight has a mass greater than the mass of said second weight. 18. An earth compacting machine according to claim 17 including means to rotate said second weight at a speed greater than said first weight. 19. An earth compacting machine according to claim 10 wherein said first weight is mounted on a first shaft; said second weight is mounted on a second shaft; motor means rotates one of said shafts; and drive means between said shafts for rotating said other shaft in response to rotation of said one shaft. 20. An earth compacting machine according to claim 19 wherein said weights are rotated and positioned relative to each other such that both weights occupy a top vertical position simultaneously during each complete revolution of one of said weights; whereby, an upwardly directed force simultaneously acts on the portions of the base of both said convex surfaces to provide an unweighting action facilitating movement of the compacting machine. 21. An earth compacting machine according to claim 19 including means for rotating one of said weights at a speed which is a multiple of the speed of rotation of the other of said weigths. 

1. A vibratory earth compacting machine including a rigid base plate comprising: a. a first bottom surface, and b. a second bottom surface spaced longitudinally of the machine from said first surface, c. both surfaces being arranged to contact said earth for compaction; d. a first weight eccentrically mounted for rotation about a first axis transverse to the machine and generally centered over said first surface, e. a second weight eccentrically mounted for rotation about a second axis transverse to the machine and generally centered over said second surface; f. first means to rotate said first weight for producing vibrations at a first frequency; g. second means to rotate said second weight for producing vibrations at a second frequency different from said first frequency; h. said rotating means including drive means for simultaneously rotating said weights in a predetermined periodically recurring pattern such that both weights occupy the same angular position on their respective axes at least once during several revolutions of one of the weights; i. said weights cooperating to vibrate said first surface of said rigid base plate at frequencies including a band of periodically recurring frequencies; and j. said weights cooperating to vibrate said second surface of said base plate at frequencies including a band of periodically recurring second frequencies different from said first frequencies.
 1. A vibratory earth compacting machine including a rigid base plate comprising: a. a first bottom surface, and b. a second bottom surface spaced longitudinally of the machine from said first surface, c. both surfaces being arranged to contact said earth for compaction; d. a first weight eccentrically mounted for rotation about a first axis transverse to the machine and generally centered over said first surface, e. a second weight eccentrically mounted for rotation about a second axis transverse to the machine and generally centered over said second surface; f. first means to rotate said first weight for producing vibrations at a first frequency; g. second means to rotate said second weight for producing vibrations at a second frequency different from said first frequency; h. said rotating means including drive means for simultaneously rotating said weights in a predetermined periodically recurring pattern such that both weights occupy the same angular position on their respective axes at least once during several revolutions of one of the weights; i. said weights cooperating to vibrate said first surface of said rigid base plate at frequencies including a band of periodically recurring frequencies; and j. said weights cooperating to vibrate said second surface of said base plate at frequencies including a band of periodically recurring second frequencies different from said first frequencies.
 2. A vibratory earth compacting machine according to claim 1 wherein said first weight is adapted to rotate at an essentially constant speed; said second weight is adapted to rotate at an essentially constant speed which is one-half the speed of rotation of said first weight; and both weights occupy the same vertical position on their respective axes at least once during several revolutions of one of the weights.
 3. A vibratory earth compacting machine according to claim 1 wherein said first surface of said base plate is convex; said second surface of said base plate is convex; and said second weight has a greater mass than said first weight.
 4. A vibratory earth compacting machine according to claim 2 wherein said second surface is on a portion of the base plate having a greater mass than the portion of the base plate having said first surface.
 5. A vibratory earth compacting machine comprising: a. a rigid base plate having a plurality of arcuate convex bottom portions formed in said plate and arranged to contact the earth for compaction, b. said arcuate portions extending transversely to the machine and being disposed longitudinally with respect to each other, c. vibrating means mounted on said base plate for vibrating said plate, and d. said vibrating means being disposed in spaced relation above said arcuate portions.
 6. A compacting machine as defined in claim 5 wherein a rigid frame member is spaced above said base plate, said frame member being supported by spring means from said base plate.
 7. A compacting machine as defined in claim 6 wherein a power drive means is mounted on said frame member to drive said vibrating means.
 8. A compacting machine as defined in claim 5 wherein said vibrating means includes a vibrating mechanism disposed above each said arcuate portion.
 9. A compacting machine as defined in claim 5 wherein said arcuate portions include a first arcuate portion having a greater mass than a second arcuate portion.
 10. A compacting machine as defined in claim 5 wherein said vibrating means includes a first vibrating means and a second vibrating means, said first vibrating means includes a first weight eccentrically mounted for rotation about a first axis, and said second vibrating means includes a second weight eccentrically mounted for rotation about a second axis.
 11. A coMpacting machine as defined in claim 10 wherein said first axis is disposed in a vertical plane which includes the center of curvature of a first arcuate portion, and said second axis is disposed in a vertical plane which includes the center of curvature of a second arcuate portion.
 12. A compacting machine as defined in claim 5 wherein said vibrating means includes a first vibrating and a second vibrating means, and means to operate said first and second vibrating means at different frequencies.
 13. An earth compacting machine according to claim 9 wherein said vibrating means includes a first and second vibrating means, and means for operating said second vibrating means at a higher frequency than said first vibrating means.
 14. A compacting machine as defined in claim 9 wherein said vibrating means includes a first vibrating means and a second vibrating means, and means to operate said first and second vibrating means at different frequencies.
 15. An earth compacting machine according to claim 12 wherein said first frequency is approximately one-half second frequency.
 16. An earth compacting machine according to claim 12 wherein said first means includes a first weight mounted eccentrically for rotation; said second means includes a second weight mounted eccentrically for rotation; and said operating means includes means to rotate said weights at different speeds relative to each other.
 17. An earth compacting machine according to claim 10 wherein said first weight has a mass greater than the mass of said second weight.
 18. An earth compacting machine according to claim 17 including means to rotate said second weight at a speed greater than said first weight.
 19. An earth compacting machine according to claim 10 wherein said first weight is mounted on a first shaft; said second weight is mounted on a second shaft; motor means rotates one of said shafts; and drive means between said shafts for rotating said other shaft in response to rotation of said one shaft.
 20. An earth compacting machine according to claim 19 wherein said weights are rotated and positioned relative to each other such that both weights occupy a top vertical position simultaneously during each complete revolution of one of said weights; whereby, an upwardly directed force simultaneously acts on the portions of the base of both said convex surfaces to provide an unweighting action facilitating movement of the compacting machine. 